CONTRIBUTION INDEX OF LAND COVER AND LAND SURFACE TEMPERATURE CHANGES IN UPPER HILL NAIROBI, KENYA

P W Mwangi,P K Kamau,F N Karanja,S C Letema

doi:10.5194/isprs-annals-v-3-2021-141-2021

Abstract

Abstract. Urban heat island is the difference in thermal temperature between rural and urban areas. The urbanization process alters the material type with impervious surfaces being absorbers of incoming radiation during the day and emitting it at night. The research involved the use of time-series satellite imagery from Sentinel, Landsat, ASTER and MODIS for the period 1986, 1995, 2000, 2005, 2011, 2015 and 2017 over the Upper Hill, Nairobi. Morning, afternoon and night land surface temperatures (LST) were calculated for each of these years and analyzed together with the land cover. The mean albedo was calculated to determine the relationship between each land cover and mean LST. The contribution index was calculated to determine whether a land contributed positively or negatively to the mean LST in Upper Hill. Results indicated that built-up land cover had increased from 1986 to 2017 by 0.86% per annum while forest land cover had decreased by 0.99% per annum. Sparse grassland had higher albedo and LST values of 0.81 and 27.9 °C respectively, whereas water had lower albedo and LST values of 0.09 and 25.1 °C. Water had the lowest mean LST during the day but highest mean LST in the afternoon and night in each of the years due to its high thermal capacity. Bare ground tends to have a higher contribution index compared to other land covers, while forest land cover has a negative contribution index, indicating the impact land cover types have on LST and the urban heat island effect.

Highlights

Human activities have led to irreversible changes to the ecosystem and it is likely that further damage will occur (Schipper et al, 2010)
Land cover changes from 1986 to 2017 showed an increase in builtup land cover of 0.86% per annum while forest land cover decreased by 0.99% per annum
This paper investigated the relationship between changes of land cover on land surface temperature and its effect on the contribution index

Summary

Introduction

Human activities have led to irreversible changes to the ecosystem and it is likely that further damage will occur (Schipper et al, 2010). Whether or not causes of climate change can be attributed to anthropogenic activities, it is evident that there are new climate and weather patterns. This potentially puts urban residents at risk, affecting their health and wellbeing, while stressing the environment, buildings and other assets (Carmin et al, 2012). Urban heat islands (UHI) has been intensively studied and involves computing the differences in surface and air temperature between nearby rural and urban areas (Zhan et al, 2015). The land surface temperature (LST), which considered an important parameter in urban climate, directly controls UHI (Feizizadeh & Blaschke, 2013)

Methods

Results

Conclusion